Mating of Similar Parts 137 



we cannot explain the process as due to the gradually diver- 

 gent development of two nuclei, one in the male direction, 

 the other in the female direction, till they have become so 

 diverse as to be unbalanced, and so to require reunion. And 

 there is no ground on this basis for any rejuvenescence to be 

 produced by the union ; for the male and female parts that 

 become united were already in union before the separation 

 and reunion occurred. 



A modified form of this notion is held by some students, 

 a form so modified as to be almost if not quite empty. In 

 such a case of reunion of two half nuclei of a single cell 

 as we see in Figure 41, as well as in all other cases, it is 

 maintained that the two half nuclei have become diverse, in 

 the divisions that have just occurred, one retaining more 

 of the kinetic or male characteristics, the other more of the 

 vegetative or female characteristics ; and that this is the 

 reason why the two now unite. That is, after the two half 

 nuclei have separated, this theory if correct gives a ground 

 for their reuniting. But it gives no ground at all for the 

 fact that the organism periodically goes through this whole 

 process, of separating off two half nuclei, which then again 

 unite, since what is accomplished by their union was al- 

 ready existent before the process occurred. And it gives 

 no ground for expecting any rejuvenescence or other marked 

 physiological result from mating. That is, it gives no ex- 

 planation for periodic mating such as is given for periodic 

 taking of food, when we show that it is the taking of food 

 that makes possible the activities and growth of organisms. 

 It is therefore not surprising that in a paper maintaining 

 this theory, Hartmann (1909) concludes with the statement 

 that he thinks it most improbable that this will turn out to 

 be the full explanation of the matter. 



On the whole, it appears that in Paramecium and many 



